Table 19.1 provides short summaries of some vulnerabilities which, in the judgment of the authors of this chapter and in the light of the WGI AR4 and chapters of the WGII AR4, may be considered ‘key’ according to the criteria set out above in Section 19.2. The table presents vulnerabilities grouped by the following categories, described in the following text:

Global social systems

Regional systems

Global biological systems

Geophysical systems

Extreme events

The table attempts to describe, as quantitatively as the literature allows, how impacts vary with global mean temperature increase above 1990-2000 levels. In addition, the authors of this chapter have assigned confidence estimates to this information. Where known, the table presents information regarding the dependence of effects on rates of warming, duration of the changes, exposure to the stresses, and adaptation taking into account uncertainties regarding socio-economic development. However, only in a few cases does the literature address rate or duration of warming and its consequences. As entries in the table are necessarily short, reference should be made to the relevant chapters and to the accompanying text in this chapter for more detailed information and cross-referencing, including additional caveats where applicable.

Table 19.1. Examples of potential key vulnerabilities. This list is not ordered by priority or severity but by category of system, process or group, which is either affected by or which causes vulnerability. Information is presented where available on how impacts may change at larger increases in global mean temperature (GMT). All increases in GMT are relative to circa 1990. Entries are necessarily brief to limit the size of the table, so further details, caveats and supporting evidence should be sought in the accompanying text, cross-references, and in the primary scientific studies referenced in this and other chapters of the AR4. In many cases, climate change impacts are marginal or synergistic on top of other existing and changing stresses. Confidence symbol legend: *** very high confidence, ** high confidence, * medium confidence, • low confidence. Sources in [square brackets] are from chapters in the WGII AR4 unless otherwise indicated. Where no source is given, the entries are based on the conclusions of the Chapter 19 authors.

Although some risks would be reduced, aggregate health impacts would increase, particularly from malnutrition, diarrhoeal diseases, infectious diseases, floods and droughts, extreme heat, and other sources of risk */**. Sensitive to status of public health system *** [8.ES, 8.3, 8.4, 8.6].

Stresses such as increased drought, water shortages, and riverine and coastal flooding will affect many local and regional populations **. This will lead in some cases to relocation within or between countries, exacerbating conflicts and imposing migration pressures * [19.2].

Tens of millions of people at risk ofincreased water stress; increased spread of malaria • [9.2, 9.4.1, 9.4.3].

Hundreds of millions of additional people at risk of increased water stress; increased risk of malaria in highlands; reductionsin crop yields in many countries, harm to many ecosystemssuch as Succulent Karoo • [9.4.1, 9.4.3, 9.4.4, 9.4.5].

Tens of millions of people at risk of water shortages • [13.ES, 13.4.3]; many endemic species at risk from land-use and climate change • (~1ºC) [13.4.1, 13.4.2].

More than a hundred million people at risk of water shortages •[13.ES, 13.4.3]; low-lying coastal areas, many of which are heavily populated, at risk from sea-level rise and more intensecoastal storms • (about 2-3ºC) [13.4.4]. Widespread loss of biodiversity, particularly in the Amazon • [13.4.1, 13.4.2].

Continued warming likely to lead to further loss of ice cover andpermafrost ** [15.3]. Arctic ecosystems further threatened **,although net ecosystem productivity estimated to increase **[15.2.2, 15.4.2]. While some economic opportunities will open up (e.g., shipping), traditional ways of life will be disrupted ** [15.4, 15.7].

Carbon cycle feedback increases projected CO2 concentrations by 2100 by 20-220 ppm for SRES[2] A2, with associated additional warming of 0.1 to 1.5°C **. AR4 temperature range (1.1-6.4°C) accounts for this feedback from all scenarios and models but additional CO2 and CH4 releases are possible from permafrost, peat lands, wetlands, and large stores of marine hydrates at high latitudes * [4.4.6, 15.4.2].